The present invention relates to a tool for well workovers, and more specifically relates to an integrated sidetrack drilling tool.
A sidetrack drilling tool comprises a whipstock and a milling cone for downhole sidetrack drilling. The whipstock and the milling cone of a conventional sidetrack drilling tool are two separate tools. To perform sidetrack drilling, the whipstock is first mounted onto a feeder and then fed to a predetermined position in the downhole by using a drilling device; next, an inclined surface of the whipstock is adjusted in terms of its orientation as required by the specific design of the sidetrack drilling; after that, fix the whipstock in the downhole by hydraulic or mechanical setting, and then separate the feeder and the whipstock by rotating or pulling and pressing the drilling device; finally, retrieve the drilling device and the feeder and mount the milling cone for sidetrack drilling. Since a sidetrack drilling well is quite deep, it is costly, time consuming and labor intensive every time to descend the drill and then retrieve it up again.
In order to overcome the problems existing in the conventional sidetrack drilling tool and to enhance operating efficiency, both Chinese patent publications under numbers CN2679348 and CN201756914 disclose an integrated drilling device for casing. However, the integrated drilling device for casing as disclosed is restrained by the dimensions of the wellbore, the whipstock and the milling cone, and thus requires more precise coaxiality in the connection between the milling cone and the whipstock. In CN2679348, the milling cone and the whipstock are fixedly connected by screws; since an upper end of the whipstock is a wedge shape end with a pointed tip, a more deviated coaxiality in the connection between the milling cone and the whipstock is resulted, thereby causing much difficulty in descending the drilling device down the well and often causing accidental falling of the whipstock. In CN201756914, the milling cone and the whipstock are connected by a connection sleeve; restrained by the dimensions of the whipstock and the milling cone and the fact that the connection sleeve has to be milled away before drilling an opening, the connection sleeve can only be made thinner and therefore being susceptible to deformation when descending down the well; accordingly, a more deviated coaxiality in the connection between the milling cone and the whipstock is resulted, thereby obstructing the drilling device from descending down to the predetermined position; in fact, no drilling device in this kind of structure has ever been successfully applied in actual practice. Furthermore, the integrated drilling device for casing as disclosed by the two Chinese patent publications has its center of the milling cone being a straight-through axial hole; since this kind of structure cannot release the surge pressure generated by the drilling fluid inside the drilling rod when descending the drilling device, surge pressure generated by obstruction when descending the drilling device can move the slips easily and thereby resulting in improper setting; accordingly, setting will fail and even the well bore has to be abandoned.